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Science/Tech See other Science/Tech Articles Title: Scientists Chart Record Rise In Yellowstone Caldera The floor of Yellowstone National Park's gigantic volcano has been rising at a record rate in recent years, probably due to an underground blob of molten rock more than 14 times the size of Billings, according to a new study. The Yellowstone caldera rose nearly 3 inches a year for the past three years, faster than anyone has ever recorded. "These are rates three times (greater) than previous historic rates," said University of Utah seismologist Bob Smith, a lead author of the study to be published in the journal Science today. But that rapid rising isn't an indication of an imminent volcanic eruption or hydrothermal explosion at Yellowstone, he said. It appears in line with behavior at other volcanic craters that rise and fall for thousands of years without large-scale, catastrophic eruptions. "These things go up and down," Smith said. "That's very common for calderas globally." The researchers believe the 463-square-mile slab formed from molten rock in the magma chamber beneath Yellowstone, causing the surface of the caldera to rise. That intrusion of molten rock, believed to have happened in mid-2004, only added to the force of the huge plume of magma that begins some 400 miles underground, roughly beneath Dillon, and tilts toward Yellowstone, ending about 30 miles below the surface, where it widens to about 300 miles across. The Yellowstone "hot spot" provides energy for the planet's largest collection of geysers and hot springs and constant, roiling influence on the largest volcanic field in North America. The caldera has probably been rising and falling for about 15,000 years. Smith and others have been tracking it closely. In recent years, the work has been aided by data collected from satellites. Portions of the caldera rose more than 3 feet between 1923 and 1984, then dropped nearly 8 inches from 1985 to 1995. Measurements in 1995 and 1996 showed it rising again before starting to fall in 1997. The caldera suddenly reversed course in July 2004, noticeably at Mallard Lake Dome, west of Yellowstone Lake's West Thumb, and at Sour Creek Dome north of Fishing Bridge. The rapid rise continued steadily until about six months ago, when it started to slow. "Our best evidence is that the crustal magma chamber is filling with molten rock," Smith said. "But we have no idea how long this process goes on before there either is an eruption or the inflow of molten rock stops and the caldera deflates in again." Steam and hot water also play a role in pushing the caldera up, Smith said, but probably to a lesser degree than the injection of molten rock. A few inches of inflation at the caldera may not sound like much, but the caldera has been moving at a faster clip than horizontal movements along California's San Andreas Fault. Still, it's tough to tease out what it will all mean for Yellowstone's complex and dynamic system. "We only have a few decades of high-quality data, and the system is 2 million years old," Smith said. "So trying to predict what its future is ... you have to be pretty careful." Just outside the caldera, another bulge has been decreasing since 2004. The dome, called the North Rim Uplift, is near Norris Geyser Basin. Between 1997 and 2003, it grew by about 5 inches and may have been behind unusual thermal activity in the area, including a sudden rise in temperatures, formation of new steam vents and the reawakening of Steamboat geyser, the world's tallest. But in 2004, the dome began deflating and activity died down. Smith and others suspect there's a connection between that falling dome and the rising caldera, but it's still unclear exactly what it is. Jacob Lowenstern, scientist-in-charge of the Yellowstone Volcano Observatory, said the ability to collect data on the caldera has improved dramatically in recent years, but it's still difficult to discern what's happening miles below the park's surface. "You can see what an alive system this is," Lowenstern said.
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